KR0178831B1 - zoom lens - Google Patents

Abstract

The zoom lens according to the present invention comprises a first lens group having a positive refractive power and a second lens group having a negative refractive power, facing the zooming by changing the distance between the two lens groups, and the first lens group having at least two positive lenses; With at least two negative lenses, the distance from the first lens surface to the final lens surface in the telephoto end, the diagonal length of the effective screen of the image frame, and the shortest and longest focal length of the whole are determined appropriately.

Description

zoom lens

1 (a), (b) and (c) are lens block diagrams of the first numerical embodiment of the present invention.

2 (a), (b) and (c) are lens block diagrams of the second numerical embodiment of the present invention.

3A, 3B and 3C are lens block diagrams of a third numerical embodiment of the present invention.

4A, 4B, and 4C are lens block diagrams of a fourth numerical embodiment of the present invention.

5A, 5B and 5C are lens block diagrams of a fifth numerical embodiment of the present invention.

6A, 6B and 6C are lens block diagrams of a sixth numerical embodiment of the present invention.

7 is aberration curves of the wide-angle end of the first numerical embodiment of the present invention.

8 is an aberration curve at an intermediate position of the first numerical embodiment of the present invention.

9 is aberration curves of the telephoto end of the first numerical embodiment of the present invention.

10 is aberration curves of the wide-angle end of the second numerical embodiment of the present invention.

11 is an aberration curve at an intermediate position of the second numerical embodiment of the present invention.

12 is the aberration curve of the telephoto end of the second numerical embodiment of the present invention.

13 is the aberration curve of the wide-angle end of the third numerical embodiment of the present invention.

14 is an aberration curve at an intermediate position of the third numerical embodiment of the present invention.

15 is the aberration curve of the telephoto end of the third numerical embodiment of the present invention.

16 is the aberration curve of the wide-angle end of the fourth numerical embodiment of the present invention.

17 is an aberration curve at an intermediate position of the fourth numerical embodiment of the present invention.

18 is aberration curves of the telephoto end of the fourth numerical embodiment of the present invention.

19 is aberration curves of the wide-angle end of the fifth numerical embodiment of the present invention.

20 is the aberration curve of the intermediate position of the fifth numerical embodiment of the present invention.

21 is aberration curves of the telephoto end of the fifth numerical embodiment of the present invention.

22 is aberration curves of the wide-angle end of the sixth numerical embodiment of the present invention.

23 is aberration curves at intermediate positions in the sixth numerical embodiment of the present invention.

24 is the aberration curve of the telephoto end of the sixth numerical embodiment of the present invention.

* Explanation of symbols for main parts of the drawings

d: d line g: g line

S: Medium image focus M: Meridian focus

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zoom lens composed of two lens groups suitable for a lift shutter type camera, a video camera, or the like. In particular, by appropriately setting the lens configuration of each lens group, aberration correction can be performed satisfactorily and the entire lens can be provided. The present invention relates to a zoom lens having a wider angle of view and a zoom ratio of about 2.4 to 2.7 by shortening the length (the distance from the front vertex to the top surface).

In recent years, with miniaturization of lift shutter type cameras, video cameras, and the like, zoom lenses having a short overall length of a lens have been demanded. In the technical field of compact cameras that do not replace lenses such as lift shutter type cameras, a zoom lens is also desired to be mounted. In particular, there is a need for a zoom lens having a distance equivalent to that of a conventional short focal length lens.

A small zoom lens for zooming can be manufactured by forming the first lens group having the positive refractive power and the second lens group having the negative refractive power back and forth and changing the distance between the two lens groups. This is called so-called two-group zoom lens, and is proposed in JP-A-57-201213, JP-A-60-170816, JP-A-60-191216 and JP-A 62-56917. have.

In this publication, positive and negative refractive power arrangements are adopted in order from the object side, and the back focus distance is made relatively short, thereby achieving a two-group zoom lens having high optical performance which aims to shorten the entire lens length.

In addition, Japanese Patent Application Laid-Open No. 62-284319, Japanese Patent Application Laid-Open No. 62-256915, Japanese Patent Application Laid-Open No. 64-52111, Japanese Patent Application Laid-Open No. 1-193807, etc. A two-group zoom lens is disclosed, which comprises a group of second lens groups of sub-refractive power and changes the distance between both lens groups so that both lens groups are axially moved forward from the wide-angle end to the telephoto end to zoom.

In addition, Japanese Patent Application Laid-Open No. 63-161422 discloses a zoom lens having a wide angle of view of about 55 degrees, in which the first lens group is composed of five lenses: positive, negative, negative, positive and positive. Is disclosed.

In addition, in Japanese Patent Application Laid-Open No. 62-90611, Japanese Patent Application Laid-Open No. 62-l13120, and Japanese Patent Application Laid-Open No. 3-116110, the first lens group is defined by lenses in positive, negative, negative, and positive four. A two-group zoom lens having a zoom ratio of about 1.5 is disclosed.

In addition, Japanese Patent Laid-Open No. 2-284109 discloses that the first lens group is composed of five lenses of positive, negative, negative, positive, and positive, and the second lens group is composed of three lenses of positive, negative, and negative. The configured two-group zoom lens is disclosed.

In addition, Japanese Patent Laid-Open No. 3-175409, Japanese Patent Laid-Open No. 4-22911, and Japanese Patent Laid-Open No. 5-19166 disclose that the first lens group includes two or more positive lenses and three or more negative lenses. The configured two-group zoom lens is disclosed.

The use of the two-lens zoom lens having the first lens group of the positive refractive power and the second lens group of the sub-refractive power of the above-described form allows the entire lens system to be miniaturized and has a zoom ratio of about 2.4 to 2.7 and is good over the entire zooming range. In order to obtain optical performance, it is necessary to appropriately set the configuration rules for the structure and arrangement of the lens structure of each lens group.

In general, when the refractive power of the first lens group and the second lens group is strengthened, the amount of movement of each lens group due to zooming is reduced, which may shorten the overall length of the entire lens system.

However, if the refractive power of each lens group is strengthened without any countermeasures, the aberration fluctuation due to zooming becomes larger, which causes a problem that it is difficult to correct.

In the present invention, a so-called two-group zoom lens is used, and design rules for the structure and arrangement of the lens configuration of each lens group are appropriately set. In particular, it has a wide angle of view with a zoom ratio of 2.4 to 2.7, and shortens the entire lens length. Therefore, it is an object of the present invention to provide a zoom lens having an improved compact shape by stably maintaining high optical performance over the entire zooming range.

The zoom lens according to the present invention comprises a first lens group of positive refractive power and a second lens group of negative refractive power in order from the object side. A zoom lens that zooms by varying an interval between the first lens group and the second lens group, wherein the first lens group has at least two positive lenses and at least two negative lenses. In the telephoto end, when the axial distance from the first lens surface to the final lens surface is DLT, the diagonal length of the effective screen of the image frame is LY, and the shortest and longest focal lengths of the entire system are fW and fT, respectively. Satisfy the condition.

These and other features will be apparent from the following description taken in conjunction with the drawings.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

1 (a), 1 (b), 1 (c) to 6 (a), 6 (b) and 6 (c) are the first of the zoom lens of the present invention, respectively. It is a longitudinal cross-sectional view of a 6th numerical example. In these figures, the end of the reference numeral (A) denotes the wide-angle end, the (B) denotes the intermediate focal length position, and the (C) denotes the zoom position of the telephoto end.

In the lens diagram, L1 is a first lens group of positive refractive power, L2 is a second lens group of negative refractive power, and the distance between the first lens group and the second lens group is simultaneously reduced to thereby reduce both the first lens group and the second lens. As shown by arrow 2, the group is axially moved forward to zoom from the wide-angle end to the telephoto end. The diaphragm SP is disposed on an image surface side of the first lens group and moves together with the first lens group. IP is on the top.

In this embodiment, such a zooming method is used, and the above-described rule is adopted to shorten the overall length of the whole system. In particular, by widening the angle of view at the wide-angle end and shortening the entire lens length, the zoom ratio is taken at about 2.4 to 2.7, and the aberration fluctuations due to the zooming are well corrected to obtain high optical performance over the entire zooming range.

Also, based on the above conditional expressions (1) and (2), the ratio between the lens length DLT (distance from the first lens surface to the final lens surface) and the longest focal length fT at the telephoto end of the entire lens system. And the ratio between the diagonal length LY and the shortest focal length fW of the effective screen of the upper frame, thereby reducing the diameter of the front lens member to reduce off-axis aberration such as coma aberration at the wide-angle end. Correct it well.

If the upper limit of the conditional expression (1) is exceeded, the lens length of the lens system in the telephoto end is too long and the front lens diameter increases, which is not preferable. If the lens length of the entire lens system in the telephoto end is too short beyond the lower limit, coma aberration and other off-axis aberrations are generated at the wide-angle end, making it difficult to correct.

If the shortest focal length fW becomes too short for the diagonal length LY of the effective frame of the upper frame because the upper limit of the conditional expression (2) is too large, or the angle of view at the wide-angle end becomes too wide, the image is zoomed at the wide-angle end. It becomes difficult to maintain good optical performance of the entire screen of the frame, and the lens diameter increases, which is undesirable. If the shortest focal length is too long or the angle of view at the wide-angle end is too narrow beyond the lower limit, the overall length increases, which is not desirable, and other predetermined zoom ratios cannot be secured.

In addition, the present invention satisfies the following features or conditions in order to miniaturize the entire lens system and obtain high optical performance over the entire zooming range.

(1-1) For the first lens group, the distance DL1 from the first lens surface to the final lens surface is in the following range:

In the range exceeding the upper limit of the conditional expression (3), the front lens diameter increases in proportion to the lens length DL1 of the first lens group. In addition, if the lens length DL1 of the first lens group becomes too short in excess of the lower limit, it is difficult to properly correct the off-axis aberration at the wide-angle end, which is undesirable.

(1-2) In the negative lens of the first lens group, the lens surface on the image surface side of the foremost lens is formed on an aspherical surface in which the negative refractive power becomes stronger as it comes from the lens center to the edge, The lens surface is formed at the radius of curvature RaF and satisfies the following conditional expression:

The above conditional expression (4) aims at satisfactorily correcting coma, flare and other aberrations at the wide-angle end when the aspherical surface is applied to at least one lens surface in the front of the negative lens group of the first lens group. If one of the upper limit and the lower limit of the conditional expression (4) is exceeded, it is difficult to correct the coma and flare at the wide-angle end.

(1-3) The first lens group includes a meniscus-shaped positive lens having a convex surface facing an object axis, a negative lens having a concave shape with both lens surfaces, and a strong refractive index surface facing an image surface stronger than an object side. Both lenses have a convex positive lens, at least one negative lens, and a positive lens having a convex positive lens directed toward a strong refractive surface on the image surface side as compared with the object side.

As used herein, the at least one negative lens is a meniscus-shaped negative lens facing the convex surface on the object side, or a meniscus-shaped negative lens facing the convex surface on the image side and a convex surface on the object side. A meniscus-shaped negative lens facing the lens is referred to. As a result, aberration fluctuations due to zooming are corrected well to obtain high optical performance over the entire zooming range and the entire screen of the image frame.

(1-4) The second lens group is composed of a meniscus-type positive lens facing the convex surface on the image side and one or two negative lenses of the meniscus shape facing the concave surface on the object side. .

Note that in the present invention, instead of satisfying the above-described features or conditions, the lens group may be configured as follows. Even in this case, it is possible to achieve a zoom lens which is an object of the present invention.

(2-1) A zoom lens which zooms by changing a distance between two lens groups by forming a first lens group of positive refractive power and a second lens group of negative refractive power back and forth, wherein the first lens group comprises at least two positive lenses. And at least two negative lenses, and the foremost lens in the negative lens of the first lens group has an aspherical surface in which the negative refractive power becomes stronger as it comes from the center of the lens to the edge. If the refractive index of the material is NaL, the following conditional expression is satisfied:

As a result, the entire lens system can be miniaturized to obtain high optical performance over the entire zooming range. Here, the conditional expression (5) mainly sets aberrations such as image curvature by appropriately setting the refractive index of the material of the negative lens by making at least one lens surface of the foremost lens in the negative lens of the first lens group an aspherical surface. Correctly correct. Outside the conditional equation (5), the Petzval sum increases in the negative direction, and the top surface curvature becomes significant. It is preferable to satisfy the following characteristics or conditions in the structure of the said characteristic, and for the improvement of aberration correction.

(2-2) The foremost lens in the negative lens of the first lens group consists of a material whose Abbe number is in the following range:

The conditional expression (6) aims to impart an appropriate range to the Abbe number of the material of the negative lens to which the aspherical surface is applied, and to mainly correct magnification chromatic aberration well over the entire zooming range. Deviation from the above conditional expression (6) makes it difficult to properly correct variations in magnification chromatic aberration due to zooming.

(2-3) The aspherical surface of the foremost lens in the negative lens of the first lens group is the lens surface on the image side, and the radius of curvature RaF of the lens surface on the object side of the foremost negative lens is expressed by the following conditional expression. Satisfies:

Where fT is the longest focal length of the whole system.

The above conditional expression (7) aims at satisfactorily correcting coma, flare and other aberrations at the wide-angle end when an aspherical surface is applied to at least one lens surface of the lens in front of the negative lens of the first lens group. If any one of the upper limit value and the lower limit value of the conditional expression (7) is exceeded, it is difficult to correct the coma and flare at the wide-angle end.

(2-4) The first lens group is a meniscus-shaped positive lens with convex surfaces facing the object side, a negative lens having both concave shapes, and a strong refractive index surface with an image surface stronger than the object side. The positive lens has a convex positive lens, the positive lens having at least one negative lens, and the positive lens having a strong refractive surface toward the image side as compared with the object side.

As used herein, the at least one negative lens is a meniscus-shaped negative lens facing the convex surface on the object side, or a meniscus-shaped negative lens facing the convex surface on the image side and a convex surface on the object side. A meniscus-shaped negative lens facing the lens is referred to. As a result, aberration fluctuations due to zooming are corrected well to obtain high optical performance over the entire zooming range and the entire screen of the image frame.

(2-5) The second lens group is composed of a meniscus-type positive lens facing the convex surface on the image side and one or two negative lenses of the meniscus shape facing the concave surface on the object side. do.

Next, the first to sixth numerical examples of the present invention are shown. In the numerical data of the first to sixth numerical embodiments, Ri is the radius of curvature of the i-th lens surface from the object side, Di is the i-th lens thickness or air space from the object side, and Ni and υi are respectively from the object side. The refractive index and Abbe number of the material of the i-th lens element. Table 1 shows the numerical values in the above Conditional Expressions (1) to (6) for the first to sixth numerical examples.

The aspherical shape is represented by the following equation with the X axis in the axial direction, the H axis in the direction perpendicular to the optical axis, and the traveling direction of the light to be positive:

According to the present invention, by applying the shape of the zoom lens which zooms by moving two lens groups having a predetermined refractive power, and setting the lens configuration of each lens group as described above, the zoom ratio is about 2.4 to 2.7. In addition to shortening, high optical performance can be stably maintained over the entire zooming range.

Claims (8)

A zoom lens configured to zoom by forming a first lens group of positive refractive power and a second lens group of negative refractive power back and forth and varying the distance between the two lens groups, wherein the first lens group comprises at least two positive lenses and at least two. Two negative lenses, DLT as the distance from the first lens surface to the final lens surface in the telephoto end, LY as the diagonal length of the effective picture of the image frame, and fW and fT as the shortest and longest focal lengths of the whole system, respectively. A zoom lens characterized by satisfying the following conditional expression: 0.22DLT / fT0.43 1.31LY / fW1.88. The zoom lens according to claim 1, wherein the following conditional expression is satisfied. 0.09 DL1 / fT / 0.27 (wherein DL1 is the distance from the first lens surface to the final lens surface of the first lens group). 2. The lens surface of claim 1, wherein the lens surface on the image surface side of the foremost lens in the negative lens of the first lens group is formed as an aspherical surface in which the negative refractive power becomes stronger as it comes from the lens center to the edge, and the lens surface on the object side is curvature. A zoom lens formed of a radius RaF and satisfying the following conditional expression: -0.37RaF / fT-0.11. 2. The first lens group according to claim 1, wherein the first lens group has a meniscus-shaped positive lens having a convex surface facing the object side, a negative lens having a concave shape with both lens surfaces, and a strong refractive index surface having a stronger image surface side than the object side. The zoom lens according to claim 1, wherein the positive lens has a convex positive lens, the positive lens having a convex shape, at least one negative lens, and a strong refracting surface directed toward the image side in comparison with the object side. A zoom lens that zooms by changing a distance between two lens groups by forming a first lens group of positive refractive power and a second lens group of negative refractive power back and forth, wherein the first lens group comprises at least two positive lenses and at least two negative lenses. A lens having a lens, and the frontmost lens in the negative lens of the first lens group has an aspherical surface in which the negative refractive power becomes stronger as it comes from the lens center to the edge, and the refractive index of the material of the frontmost lens in the negative lens Is NaL, the zoom lens according to the following conditional expression: 1.65NaL. The zoom lens according to claim 5, wherein the following conditional expression is satisfied. 49υaL (wherein υaL is the Abbe number of the material of the foremost lens in the negative lens of the first lens group). The aspherical surface of the foremost lens in the negative lens of the first lens group is the lens surface on the image side, and the radius of curvature RaF of the lens surface on the object side of the foremost negative lens satisfies the following conditional expression. Zoom lens, characterized in that. -0.37RaF / fT-0.11 (where fT is the longest focal length of the whole system). 6. The first lens group according to claim 5, wherein the first lens group has a meniscus-shaped positive lens having a convex surface facing the object side, a negative lens having a concave shape having both lens surfaces, and a strong refractive index surface stronger at the image surface side than the object side. The zoom lens according to claim 1, wherein the positive lens has a convex positive lens, the positive lens having a convex shape, at least one negative lens, and a strong refracting surface directed toward the image side in comparison with the object side.